Digitizing a recurring analog signal

Abstract

A recurring analog signal is digitized by repeatedly comparing it to a reference level, or to several reference levels, during each signal occurrence to determine where the signal has a value related to each reference level. The reference level, or levels, are changed between signal occurrences but remain constant during each occurrence. Digitization is completed after several occurrences of the signal have been analyzed in this manner.

I claim: 
     
       1. A method of digitizing a repetitive analog signal, comprising the steps of: (a) establishing a first reference voltage level and selecting a first occurrence of said analog signal,   (b) comparing the signal level of said occurrence of said analog signal with said reference voltage level,   (c) developing at each of a plurality of instants during said occurrence of the analog signal a separate digital bit whose state is a function of the relative magnitudes of the reference voltage and the analog signal at each such instant,   (d) storing said digital bits, and   (e) repeating the steps (b) through (d) on each of a plurality of subsequent occurrences of the analog signal with a different reference voltage level during each occurrence, whereby all reference voltage levels of interest within the voltage range of the analog signal are covered.   
     
     
       2. The method of claim 1 wherein step (e) includes the additional step of responding to a trigger signal to halt the generation of said digital bits, whereby the storage thereof also stops. 
     
     
       3. The method according to claim 1 wherein step (d) includes storing the bits in a high speed memory, and wherein the method that comprises the additional step of (f) processing the bits of a high speed memory between occurrences of the analog signal and storing the processed bits of the analog signal occurrence just completed in another memory, whereby said high speed memory can be used for storing the digital bits representative of another analog signal occurrence. 
     
     
       4. The method according to claim 3 which comprises the additional step of (g) displaying the processed digital bits within said another memory to show the waveform of the analog signal at a time after a sufficient number of the occurrences of the analog signal have been digitized. 
     
     
       5. A method of digitizing a repetitive analog signal, comprising the steps of: (a) establishing a first reference voltage window having an extent that is a small fraction of the voltage extent of interest of said analog signal, and selecting a first occurrence of said analog signal,   (b) comparing the voltage level of said occurrence of said analog signal with said reference voltage window,   (c) developing for each of a plurality of time intervals during said occurrence a separate digital bit whose state depends upon whether the analog signal is within the window at any time during the time interval,   (d) storing said bits in a memory, and   (e) repeating steps (b) through (d) on a plurality of subsequent occurrences of the analog signal with different and distinct reference voltage windows until the analog signal range has been scanned.   
     
     
       6. The method according to claim 5 which comprises the additional step of (f) displaying a waveform of the analog signal by modulating the intensity of a raster scan display device with the value of the bits stored in memory. 
     
     
       7. A system for digitizing an analog signal that has a plurality of successive occurrences which are substantially identical, comprising: means for establishing a reference voltage which steps through a succession of levels covering a range of the analog signal and remains at each level for at least the duration of an analog signal occurrence,   means for comparing each such reference voltage level with a distinct occurrence of the analog signal,   means receiving the results of said comparing means for developing a plurality of digital bits at a plurality of instants of time during each such signal occurrence, each of said bits reflecting whether the analog signal is above or below said reference at the instant of time at which the bit is generated, and   means receiving said bits for storing them in a digital memory, whereby a digital representation of said analog signal exists and may be utilized.   
     
     
       8. The system according to claim 7 wherein said memory means includes: a high speed memory which receives all bits for one occurrence as the bits are generated by said bit developing means,   a random access memory having a capacity much greater than said high speed memory, and   means for moving bits from said high speed memory to said random access memory between said distinct occurrences of the analog signal which are sampled, said random access memory holding all of the digital bits developed from a given analog signal.   
     
     
       9. The system according to claim 8 wherein said bit moving means includes means for loading said random access memory in a manner that the bits can be read out sequentially to form a visual display on a raster scan device. 
     
     
       10. The system according to claim 8 which additionally comprises: a raster scan display device, and   means responsive to the digital bits stored within said random access memory for driving said raster scan display device in a manner to display an analog representation of said analog signal.   
     
     
       11. The system according to claim 7 wherein said reference voltage establishing means includes a programmed microprocessor. 
     
     
       12. A system for digitizing an analog signal that has a plurality of successively occurring cycles which are substantially identical, comprising: means for establishing two reference voltages separated by a window voltage which are stepped through a succession of levels covering a range of the analog signal and remain at each level for at least the duration of an analog signal occurrence,   means for comparing each such reference voltage window with a distinct occurrence of the analog signal, and   means receiving the results of said comparison means for developing a digital bit for each of a plurality of time intervals during each distinct occurrence, each of said bits reflecting whether the analog signal is within the reference voltage window at any time during the time interval.   
     
     
       13. The system according to claim 12 which additionally comprises: a high speed memory connected to receive digital bits for one occurrence as they are generated by said digital bit developing means,   a random access memory, and   means for moving said bits from said high speed memory to said random access memory at a time between said distinct occurrences of said analog signal.